Intake Manifold Issue

[Copland]

Hi.

I have taken out my old intake manifold gasket today. I had an intermittant Code P0174 in the past. My long term fuel trims on bank 2 at idle was about +8.4 and increases randomly what put in P0174 occasionally. That's why i suspected the intake manifold gasket. The tahoe has about 111k Miles on it. As i took off the manifold, i've seen that situation shown in the picutre below. On every intake port of bank 2 i had these brown deposits. Bank 1 intake ports were totally clean. The odd on it is, that sealant surface, where the gasket touches the cylinder head, were also clean on bank 2. These brown deposits seems to have in every intake port the same pattern. What could cause this? I don't think that the old gasket was the culprit, it also seems to be fine as i took it out. Fuel trim values are also unchanged since the gasket swap. Any ideas or seen something like this before?

 

[greenhornet]

I have seen this on motorcycle intakes ,possible from fuel blow back and getting burnt on the intake port,possible restriction on that side causing poor exhaust flow,it does seem strange.

 

[andrew383]

Its oil stain from the oil that gets sucked back into the manifold from the pcv..Totally normal...This is the reason i run a catch can

Have you ever changed the o2's??

 

[Copland]

It also looked like oil to me. I was just wondering why this deposits only occur on bank 2. If it's PCV related then shouldn't the oil being spread evenly all-over every intake port, so as bank 1 as well? I already changed the upstream o2 sensor on bank2 before, didn't had any influence on the fuel trims. But i guess i messed up a little with the gasket swap. Fuel trims on both banks got a little worse after it. I think i've to take of the manifold again and double check everything. Idle is also a little rougher than before, it's not that bad but i want it as much smooth as it can be.